A number of aluminum phosphates are known. For example, U.S. Pat. No. 2,909,451 discloses the reaction of a water-soluble aluminum salt and at least a stoichiometric amount of a water-soluble orthophosphate in an aqueous medium to produce a precipitate.
Similarly, U.S. Pat. No. 3,348,910 describes the preparation of magnesium ammonium phosphate by reacting a magnesium compound such as magnesium hydroxide with an excess of monoammonium dihydrogen phosphate.
Complex phosphates are illustrated by U.S. Pat. No. 2,550,490 of the formula: EQU MM'.sub.3 H.sub.14 (PO.sub.4).sub.8.sup.. 4H.sub.2 O
where M is an alkali metal including the ammonium radical, and M' is aluminum or iron. The compounds are useful as baking acids.
Lapina et al. in the article, "NATURE OF THE COMPOUNDS FORMED ON NEUTRALIZATION OF PHOSPHORIC ACID CONTAINING ALUMINUM AND IRON BY AMMONIA", J. Appl. Chem. USSR, pp 4-7, a translation from Zhurnal Prikladnoi Khimii, Vol. 45, No. 1, pp 6-11, Jan., 1972 (Consultants Bureau, Plenum Publishing, New York), describes an ammonium aluminum phosphate in the form of rhombic platelets having the formula: NH.sub.4 Al.sub.2 (PO.sub.4).sub.2 OH.sup.. 2.5H.sub.2 O. A tabular presentation of an X-ray diffraction pattern for this material is presented. The article lacks complete information on how this phosphate was made.